1. Field of Invention
The present invention relates to a device for improved movement by the transducer head, which moves relative to a rotating or otherwise moving storage medium.
2. Background of the Prior Art
For speed and convenience, it is desirable to maximize storage capabilities on magnetic mediums such as computer disks. Although the discussion in the specification will deal primarily with magnetic disks, it works with other precise tracking systems such as video disks, laser audio disks and the like. The transducer head is controlled by a servo-system which must move the head between tracks and also must maintain the head centered over the desired track. To maintain centering or even for relatively small moves between tracks, small and precise movement is required. For larger moves, speed is important. The larger moves are referred to as the seek movements, and the smaller moves are referred to as the tracking or the fine movements. Increasing the motor size to increase he speed of seek moves makes it more difficult for the motor to make the fine movements quickly and accurately. The higher power seeking motor and the long arm that must connect the motor to the head causes high frequently mechanical resonances in the head, which limits the bandwidth for seeking to about 300 Hz. For high density magnetic mediums, a bandwidth greater than 300 Hz is needed. It is anticipated that future media will need a track pitch above 1000 tracks per inch (39 tracks/mm), which will require a tracking bandwidth over 500 Hz.
To overcome this problem, it has been proposed to use separate motors for seeking and tracking. An example is described in Lu "Floppy Disks Push Density Limits," High Technology, p. 18 (August 1983), and Ragle, U.S. Pat. No. 4,188,645 (1980). The Lu article discusses a two motor system, a course stepper motor for seek movement and a fine stepper motor for tracking movements. The "fine motor" in the Regal patent are several pair of piezo-flexure arrays. The seek motor can be a stepper motor or a linear motor. Linear motors tend to be faster but require servo mechanisms for positioning and to sense drift after the motor reaches a position. Stepper motors tend to be somewhat slower, but they do not drift. The problem with prior art two-motor systems is that the smaller motor transmits the high frequently resonances from the arm connecting the seek motor to the smaller motor, and this forces a limitation on bandwidth. Also, as a linear seek motor drifts, one must have the tracking motor compensate for the drift. There are limits, however, to the amount of compensation because the tracking motor normally has small limits of travel. Therefore, a servo system is necessary for correct position of the seek arm.
It is an object of the present invention to disclose and provide a head moving system that maximizes the effective bandwidth to provide for high track pitch, improved accuracy and faster seek times.
A key feature of the invention is mechanical isolation between the head-tracking motor combination and the seek motor and its arm to eliminate seek motor resonance from the tracking motor servo-loop to provide very high bandwidths. Specifically, the head positioning apparatus of the present invention has a fine positioning means attached to the head for moving the head through relatively small distances and a seek positioning means operably attached to the fine positioning means for moving the fine positioning means and the head through relatively large distances.
The mechanical isolator comprises a flexible connection between the fine positioner and the seek positioner. The fine positioner comprises an electromagnetic coil attached to the arm. A head support, a blade-like structure which holds the head, extends through the coil. A second magnet is mounted on the head support inside the coil, and controlled, selected application of electricity to the coil moves the magnet and the head support. A magnetic shield surrounds the coil, and the flexible members are attached near the ends of the shield. The shape of the flexible member is such that only one dimensional movement of the head and head support is allowed. Different shapes are disclosed. Various forms of shielding are also provided.
If the seek motor is a stepper motor, one will normally lock the tracking motor in its null position during seek movements. The stepper motor moves the head to the middle of the desired track, and then the tracking motor, with a servo mechanism reading position information from the disk, follows the track. With a linear seek motor, one must sense the position of the head relative to the arm of the seek motor. Sensing systems in the form of light or magnetic sensors can be used for position information. The relative position, however, is also a function of the current fed to the tracking motor. It is an object of the present invention to use tracking motor current for sensing the relative position of the head relative to the seek motor and arm.
Because ultimately, head position information is obtained from the medium, one may want to cage or lock the tracking motor in its null position during seek movements. It is an object of the present invention to do that easily and inexpensively with a minimum of parts.